1. Field of the Invention
The invention relates generally to apparatuses and methods for measuring the fluid transportation and/or absorption behavior of sheet materials and other samples.
2. Description of Related Art
The desirability and performance characteristics of numerous sheet materials depend in large part on their fluid-transportation and/or absorption behavior. For example, paper towels, tissues, and other cellulosic sheets are often evaluated by their ability to absorb water and fluids containing liquid water. Similarly, numerous fabrics have been developed for their ability to absorb and wick moisture from a surface, e.g., wick perspiration from skin. Examples of such fabrics include a weft knits, denier gradient textiles and assorted laminates such as those described in U.S. Pat. No. 5,735,145 to Pernick and U.S. Pat. No. 5,021,280 to Farnworth et al.
There are presently several methods and apparatus for determining the fluid-transportation properties of materials. For example, U.S. Pat. No. 5,138,870 to Lyssy describes an apparatus for measuring the water vapor permeability of sheet materials under adjustable constant measuring conditions. A lid having an air inlet opening and an outlet opening is attached on a cup containing water in a vapor and airtight manner. A sheet material having its circumferential border held between the rims of the cup and lid separates the water in the cup from the lid. An absorption member containing a moisture-absorbent material is in communication with the outlet opening. A blower in communication with the air inlet opening aspirates air through an air dryer and blows the resulting dry air into the sealed cup containing the sheet material. As a result, the permeability of the sheet material may be measured.
For liquid absorption testing, U.S. Pat. No. 4,357,827 to McConnell (hereinafter the “827 patent”) describes a gravimetric absorbency tester that determines the wicking properties of a material by determining the weight of liquid flowing to or from a test site. The apparatus includes a vessel for containing liquid supported solely by a balance, an indicator for indicating the weight sensed by the balance, a test surface containing the test site on which a specimen to be tested may received, a conduit operatively connecting the vessel to the test site for directing a flow of liquid between the vessel and test site, and an adjuster for vertically positioning the test site. The surface of the liquid in the vessel is maintained at a constant elevation as liquid flows into and out of the vessel.
One problematic issue associated with generally all liquid absorption testing involves the interface through which liquid is introduced into the specimen. For example, when the technology described the '827 patent is used, the test specimen is placed on a test plate having a hole though which liquid may be directed in an upward direction toward the specimen. This is problematic because fluid may preferentially wick along in the boundary between the specimen and the test plate instead of being absorbed the test specimen. In some instances, the test plate may be preferentially wetted over the specimen. Any fluid not absorbed by the specimen may represent a source of testing error.
In addition, a means may be required to provide sufficient activation energy to induce the liquid from the hole to wet the specimen and to liquid absorption by the specimen. Such means may, for example, include a pinch valve that allows liquid to be forced through the hole at a velocity that allows the liquid to contact the specimen and overcome surface forces against wetting. Such means may compromise tests designed to measure the intrinsic absorption properties of the test specimen because they introduce excess measurement noise.
Previously known technologies also have generally failed to address certain problems associated with the delivery of liquid to the specimen. For example, the technology described in the '827 patent employs a conduit operatively connecting the vessel to the test site for directing a flow of liquid between the vessel and test site. As shown in FIG. 1 of the '827 patent, the conduit defines a flow path that travels through an elevated local peak plateau region above both the vessel and the test site before reaching the test site. Such a flow path also tends to compromise tests designed to measure the intrinsic absorption properties of the test specimen because they introduce measurement errors associated with uneven or uncontrolled liquid flow. Such errors may arise, for example, due to the tendency of the conduit to trap air or other gasses.
Still another problematic issue associated liquid absorption testing is that test specimens may swell and/or deform as they absorb liquid. As a result, the test specimens in part or in whole may be displaced relative to the surface from which test specimens absorb liquid during testing. In turn, liquid transport behavior may be disrupted or otherwise altered, thereby compromising the accuracy of the test.
Accordingly, there exist opportunities to provide alternatives and improvements to known methods and apparatuses for determining the fluid-transportation properties of materials, particularly for the purpose of overcoming any shortcomings associated with known methods and apparatuses.